A range tracking system is used to provide an accurate gating pulse for an angle tracking system so that the later system receives only, or primarily, energy from a designated target. Split gate range tracking systems generally sample the incoming video signal at a first location (the early gate) and a second location (the late gate). The relative amplitudes of the two samples are used to determine whether the range gates are properly positioned to track the target. For instance, the two signal samples may be passed through substantially identical amplifying, filtering and detecting channels and applied to a difference circuit to generate a range error signal which can be used to alter the locations of the gates.
To avoid multipath and ECM interference, it is common practice to design a split gate range tracking apparatus to track on the leading edge of the target rather than on the centroid. This is accomplished by increasing the gain of the early gate channel with respect to the late gate channel. During periods when the target signal fades and only receiver noise is being gated however, this type of leading edge range tracking apparatus drifts to lower range due to the higher gain in the early gate channel. This results in loss of the target and necessitates repeated target acquisitions.